1. Field of the Invention
The present invention relates to an image recording apparatus for recording an image by fixing ink etc. on a recording medium such as paper, film, etc., and more specifically to an image recording apparatus provided with a faulty record detection unit for use in performing a recording process on the recording medium based on record data from a recording head of an image recording apparatus.
2. Description of the Related Art
As an image recording apparatus, for example, an inkjet printer discharges ink drops from a plurality of nozzles of a recording head to a recording medium held and conveyed by a conveying mechanism, and records a high quality image at a high speed.
The inkjet printer is widely utilized for office use in recording an image on a recording medium (paper) in the form of, for example, a cut sheet. Recently, the throughput of an inkjet printer can be improved by configuring a line head by arranging a number of recording heads in the direction orthogonal to the direction of conveying a recording medium, and thus the inkjet printer is also utilized for industrial use in recording an image on a recording medium (continuous paper) such as roll paper etc.
In an image recording apparatus for recording an image by fixing ink on a recording medium such as a large volume of paper, film, etc., the image can be recorded while conveying the recording medium at a high speed of several tens to several hundreds meters/min.
When the images are recorded at a high speed as described above, a verification cannot be visually made by a person as to whether or not the image data transmitted from a host apparatus matches the recorded image. Even when an image is recorded at a low speed, there can be a case where the image is not correctly verified visually by a person.
In the image recording apparatus, a recorded image is electronically read and compared with an image represented by image data from the host apparatus dot by dot, thereby detecting a faulty record.
For example, the patent document (Japanese Published Patent No. 2516606) discloses an invention of a print quality test device for use in a roll paper printer for continuously printing a picture pattern on roll paper. The device includes: a sensor device which is provided in a predetermined position in a printer, reads a picture pattern while conveying printed matter, and obtains an image signal; a device for detecting a start mark printed in advance at the head of each picture pattern while conveying printed matter; a device for obtaining the amount of a travel shift in the direction of the width of roll paper based on the fluctuation of the edge position in the direction of the width of the start mark, a device for interpolating the image signal read by the sensor device in the direction of the width of the roll paper based on the amount of a travel shift; and a device for testing the print quality of each picture pattern by comparing the corrected image signal with an image signal of a reference picture pattern.
The patent document (Japanese Published Patent Application No. H7-200792) discloses an invention of a printed matter test device for detecting in line an abnormal condition occurring on each piece of printed matter by comparing a test image obtained by sequentially taking the picture pattern of continuously traveling printed matter arranged at predetermined pitches with a predetermined reference image pixel by pixel. The device includes: a timing device for generating a timing pulse depending on the traveling speed of the printed matter; a read device for generating a sequential test image by operating according to the sampling pulse synchronous to the timing pulse, and reading a picture pattern line by line; a extraction device for selectively extracting from the sequential test image a local pattern specified in advance in the picture pattern based on the array pitch of the printed matter; an arithmetic device for performing an image arithmetic process on an extracted local pattern, and sequentially calculating the position information in a sub-pixel unit; and a synchronization device for performing a fine adjustment on the phase of a sampling pulse according to the position information, and synchronizing it with the timing pulse in a sub-pixel unit for each array pitch of the printed matter